DESCRIPTION: In spite of the overall importance of cytotoxic T-lymphocyte (CTL) responses in controlling acute and persistent viral infections, we are only one of two laboratories in the world that have concentrated one examining FIV specific responses. Peptides have been identified in the SU, TM and capsid polypeptides that induce CTL responses, but no systematic studies have been done evaluation potential epitopes in the entire sequences of these proteins. Key issues addressed in this study will be the inclusion of naturally infected, as well as experimentally infected, cats, inclusion of MHC class I preference for CTL antigenic peptides. Specific aims will be to: (1) To determine frequencies of SU, TM and capsid specific CTL in various lymphoid tissues. (2) Determine sequences of dominant and subdominant epitopes lying on these polypeptides. (3) Determine cDNA sequences encoding major histocompatibility complex (MHC) class I alpha 1 and 2 domains and correlate putative haplotype with function compatibility. (4) Identify MHC lass I anchor sites and T-ell receptor recognition sites and tolerate flexibility of the peptide sequence recognized by effector cells. (5) Redirect ongoing CTL responses with individual cats through administration of alter peptide ligands. We will evaluate animal variations expected to occur in the frequency within specific lymphoid tissues, epitope flexibility, MHC class I binding and TCR repertoire. Therefore, these studies will address very basic question crucial for future use of CTL in protecting cats in either a prophylactic or therapeutic manner.